VueJS transition on element in a loop?

Question

This is my code: I want to create a transition on the HelloWorld Component, everytime the data gets updated. The transition itself works fine

  <transition name="fade">
    <p v-if="awesome">Vue is awesome</p>
  </transition>

Here are my "cards" which are created dynamically.

  <v-row no-gutters>
    <v-col cols="12" sm="4" md="4" v-for="(todo, index) in todos" v-bind:key="index">
      <v-card class="pa-2" outlined tile>
        <transition name="fade">
          <HelloWorld
            v-bind:todos="todos"
            v-bind:index="index"
            v-bind:class="(todos[index].done)?'green':'red'"
          />
        </transition>
      </v-card>
    </v-col>
  </v-row>

Here the transition does not work.

CSS is here:

<style scoped>
.top {
  background: blue;
  color: white;
  display: flex;
  justify-content: space-around;
  border-bottom: 2.5px solid black;
}

.fade-enter {
  opacity: 0;
}

.fade-enter-active {
  transition: opacity 1s;
}

.fade-leave {
}

.fade-leave-active {
  transition: 1s;
  opacity: 0;
}
</style>

Why and how do it get it done to work?

Answer 1

If you want to animate each element in a loop, you have to:

• Put transition around the loop.
• And also, use <transition-group>, not just <transition>

<v-row no-gutters>
  <transition-group name="fade-in" mode="out-in">
    <v-col cols="12" sm="4" md="4" v-for="(todo, index) in todos" v-bind:key="index">
      <v-card class="pa-2" outlined tile>
        <HelloWorld
          v-bind:todos="todos"
          v-bind:index="index"
          v-bind:class="(todos[index].done)?'green':'red'"
        />
      </v-card>
    </v-col>
  </transition-group>
</v-row>

And I would also advise you not to use 1s long animation, it's way too long. Do something like this:

CSS

.fade-in-enter-active {
  transition: all 0.5s ease;
}

.fade-in-leave-active {
  transition: all 0.5s ease;
}

.fade-in-enter, .fade-in-leave-to {
  position: absolute; /* add for smooth transition between elements */
  opacity: 0;
}

If the animation is twitchy, you can add position: absolute; in the enter and leave-to CSS rules (or only for leave-active).

Check out this page in vue docs: https://v2.vuejs.org/v2/guide/transitions.html#List-Move-Transitions